An anchor bolt is a metal rod that is set or embedded in concrete, and has a threaded end that projects outwardly from the concrete's exterior surface. A nut threaded onto the end provides a way of bolting other structural members to such surface. The invention disclosed here has been developed for the purpose of solving certain unique problems associated with setting surface anchor bolts.
Modern-day construction often involves pouring large concrete slabs. By way of example, it is not unusual to pour slabs that cover areas as large as 7,000 square feet, or larger, at depths of 12 inches or more. It is also common for such slabs to be elevated from the ground during pouring since they are often used to construct the different levels of multiple-floor buildings. The methods for delivering, spreading and leveling the concrete for such pours are well-known, and need not be described here. However, obtaining properly set surface anchor bolts in the resultant slab or slabs has proven problematical.
Unlike concrete retainer walls and footings, where the concrete is poured between relatively closely-spaced vertical forming surfaces, placing and holding an anchor bolt in position during the pouring of concrete slabs is difficult, because of the unavailability of suitable places to mount overhead bolt-holding supports By way of comparison, in the case of a retainer wall, it is easy to place an overhead support across the top of its side forms. An equivalent device cannot be .used over concrete slabs, however, because the concrete usually spans many feet from side to side, perhaps as far as 100 feet or more.
For this reason, it was common practice in the past to set anchor bolts after both pouring and curing the slab. This was done by boring individual openings in the concrete's hardened top surface, and subsequently installing anchor bolts in each opening. Each bolt was set or fixed in place by a coalescent filler that hardened after installation, the filler typically being wet concrete or mortar.
As a practical matter, current building code requirements have made this method obsolete Consequently, builders have taken to mounting anchor bolts to the decking or forming surface underlying the slab prior to pouring. Typically, such surface is made of 3/4-inch plywood, although metal forms are also used, as well as other materials.
One method of mounting bolts to such forming surface involves using individual metal bolt-holding strips made of sheet metal. A small length at one end of such strip is bent 90.degree. relative to its remaining length, and is nailed, stapled or glued to the forming surface in a manner so that the strip extends vertically upwardly. An anchor bolt is suitably attached to the strip, sometimes by baling wire, for example, and the strip holds it in place during pouring and curing of the slab.
The problem with this type of arrangement is that it interferes with the installation of other pre-pour items. For example, post-tensioning cables, electrical conduit, plumbing, and rebar or other concrete reinforcement are all typically installed over the forming surface prior to any given pour. Installing the anchor bolts first, in the manner just described, creates a situation where both the strips and bolts get knocked around and out of place as a result of installing the other pre-pour items The end result has been poor anchor bolt placement where individual bolts have either lost their vertical alignment after the pour, or their height is incorrect relative to the concrete's top surface. Furthermore, this problem cannot be solved by installing the bolt-holding strips after the other pre-pour items, because the other items generally take up most of the space over the forming surface, making it physically impossible to have working space for attaching the holding strips.
A known improvement over the system just described involves a two-part system where an extension rod, or dog, is welded to the anchor bolt and plugged into a separate base plate that is first attached to the forming surface. The base plate takes up little space prior to and does not interfere with other prepour preparations. After such preparations are made, the dog is thereafter simply plugged into an upwardly-opening socket in the base plate, thus fixing the bolt in position for the pour.
Unlike the present invention, this last system is unwieldy because it does not provide an easy way to adjust the bolt's vertical height relative to the forming surface. Obviously, slab depth can be a variable from one slab to another. The system just described requires on-site cutting and welding of the extension dog to an appropriate length, in order to correctly set the bolt's height relative to any given slab. The labor required for doing this can represent a fairly significant cost detriment to the builder.
U.S. Pat. Nos. 1,108,859; 1,726,286; and 4,412,407 all disclose systems for holding anchor bolts. The '859 patent discloses a type of system that is significantly different from the invention disclosed here because it is not directed to holding an anchor bolt in concrete both during and after the pour. Instead, the '859 system sets a threaded anchor, minus any bolt, in place during the pour, and provides an opening through the resultant slab for extending a bolt into threaded engagement with the anchor.
The '286 patent discloses another type of metal boltholding strip that functions somewhat similarly to the boltholding strip system described above, although it has other unique drawbacks that need not be mentioned here. The '407 patent discloses a one-part anchoring system that is essentially an insert for anchoring the lower end of an externally screw-threaded bolt. Similar to the '859 patent mentioned above, the '407 insert is not intended to be used for permanently setting an anchor bolt during pouring and curing of the slab. Instead, the bolt is subsequently installed or threaded into the insert afterward.
The invention disclosed and claimed here is significantly different from the devices and systems described above. It is perhaps closest in similarity to the two-part "welded-dog" system, and offers the same advantages as such system. However, it goes further in that it provides adjustability in bolt height, and is also generally cheaper to implement These differences including their advantages, will become better understood upon consideration of the following.